What if islands threatened by rising seas didn’t drown?

Professor Paul Kench

Building a tiny replica of a Pacific island is helping scientists understand how much more resilient islands can be when faced with rising temperatures.

The outlook for coral reef island populations expecting a grim future from rising sea levels might be better than predicted, say scientists from the University of Auckland and Plymouth University in the UK.

“There’s a commonly-held belief that as sea levels go up these low-lying islands will simply be drowned and their populations will become environmental refugees,” says Professor Paul Kench, Head of the School of Environment at the University of Auckland.

But 20 years of monitoring environmental changes to islands and atolls in the Pacific and Indian Oceans is challenging this view.

“We’ve been developing evidence that islands don’t simply drown,” says Professor Kench. Instead, his research suggests, the islands will start to move on their reef platforms and sand and gravel around the coastlines will shift to form a higher and natural barrier against the sea.

A 1:50 scale replica of a coral reef island in Tuvalu, about 3000km north of New Zealand, has been constructed by the research team to support this research and demonstrate that islands on coral reefs will be more resilient to sea level rise than has been thought in the past.

The replica, which has been built in the costal basin of Plymouth’s Coastal, Ocean and Sediment Transport (COAST) laboratory, is the team’s first opportunity to isolate sea level as a variable and see the effect of half a metre to one metre rises on a whole island.

“The beauty of this experiment is that we can construct a scale model of an island that we have done a lot of work on in the Pacific and subject it gradually to sea level change and monitor how it physically will adjust.”

Coral reef islands such as Tuvalu are low-lying and sit on top of coral reef surfaces. They are the only habitable land in mid-ocean atolls and other examples are the Maldives, Chagos or Marshall Islands.

Plymouth University has been working on gravel barriers on beaches in the UK, according to Professor of Coastal Geomorphology, Gerd Masselink, and seen crest heights build up when subjected to large waves and rising sea levels.

“We are reproducing the behaviour of gravel that we have observed in the UK on our beaches and we are trying to see that same behaviour on coral reef islands that are also made of gravel,” says Professor Masselink.

The collaborative research project, funded by the Royal Society of New Zealand Catalyst Fund, will show what changes island inhabitants can expect, and how much time they will have to prepare.

Says Professor Kench: “What is really nice about these experiments is that they will … quantify precisely how these islands will change. We would expect that within 18 months to two years we will be in the position to really lay out what the future will be for many of these islands.”

Professor Paul Kench is from the School of the Environment at the University of Auckland’s Faculty of Science.